Catalan separatists clashed with Spanish police in Barcelona into the early hours of Thursday morning.

Tensions are running high as the central government steps up its efforts to stop an independence referendum scheduled for October 1.

Tens of thousands of people gathered outside the regional government’s offices after police raided the building and arrested more than a dozen local officials, including Catalonia’s junior economy minister Josep Maria Jove.

The demonstration ended with detentions and police charging against protesters.

Spanish authorities say the Catalan referendum is illegal, and they have been trying to stop it by seizing voting material — from ballot boxes to campaign literature and instruction manuals for manning voting stations.

The Constitutional Court has suspended the vote after the central government challenged its legality. Spain’s central government says the referendum goes against the 1978 constitution which states Spain is indivisible.

Polls show a minority of Catalans — though more than 40 percent — support independence, but a majority wants an opportunity to vote on the issue.